Regulating circuit

ABSTRACT

A solid state regulating circuit for a permanent magnet alternator which includes a switching element, preferably an SCR, for shunting the output winding of the alternator in response to a control signal to limit variations in power delivered to a load, and a control circuit for proving the control signal in accordance with the frequency and amplitude of the alternator output. More particularly, the control circuit may include a diode connected to the output windings of the alternator to provide a half wave signal to provide a monotonic intermediate signal of predetermined duration, and a second capacitor connecting the first capacitor and the gate of the SCR for providing the control signal for gating the SCR.

United States Patent 1191 Gynn Nov. 12, 1974 REGULATING CIRCUIT3,757,199 9/1973 Minks 322/91 x [75] Inventor: George E. Gynn, FortWayne, Ind. Primary Examiner jamcs D- Tramme" [73] Assignee: SyncroCorporation, Oxford, Mich. Attorney, Agent, or FirmHarness, Dickey &Pierce [22] Filed: Apr. 26, 1973 [57] ABSTRACT [21] Appl' 354662 A solidstate regulating circuit for 21 permanent mug- Related U.S. ApplicationData I net alternator which includes a switching element, [62] Divisionof Ser. No. 244,778. April 17, 1972. Preferably S for shunting the PPWinding Of the alternator 1n response to a control s1gnnl to limit 52us. 01 322/73, 320/61, 320/71, variations in 129Wer delivered to 9 load,and a 99mm 322/81 322/91, 322/98 circuit for proving the control signalin accordance [51] Int. Cl. H02p 9/26 with the frequency and amplitudeof the alternator [58] Field of Search 317/16; 320/71, 40, 39, OutputMore Particularly, the Control Circuit y 32O/61; 322/33, 34, 81, 73, 91,98 84 clude a diode connected to the output windings of the alternatorto provide a half wave signal to provide a 5 References Cited monotonicintermediate signalof predetermined duration, and a second capacitorconnecting the first ca- 3 278 823 L E STjATES PATENTS pacitor and thegate of the SCR for providing the con- 34021339 ll fiiiiiiiiiiiii""""'"""""::::..i?%l4 Sign for game the 3.723.844 311973Cavil 320/71 X 4 Claims, 11 Drawing Figures PATENIE HEW 1 21.9743.848177 SHEET HIF 4 amm ' PATENTEnmv 1 21974 REGULATING CIRCUIT This isa division of application Ser. No. 244,778, filed Apr. 17, 1972.

BACKGROUND AND SUMMARY OF THE INVENTION Many recreational and utilityvehicles in present use are provided with relatively low-cost permanentmagnet alternators to supply electric power for the vehicle ignition,battery and for various electrical accessories such as the vehiclelights. Since permanent magnet alternators do not utilize fieldwindings, and consequently, the field strength cannot be directlycontrolled in the usual manner by controlling the excitation of thefield winding, the regulation of the output of the permanent magnetalternator is ordinarily accomplished by a shunting circuit, forexample, as disclosed in the patent to Carmichael, et al., US. Pat. No.3,270,268. More particularly, regulation of the alternator isaccomplished by switching a relatively low impedance path across theoutput windings of the permanent magnet alternator. In the aboveCarmichael, et al. system, the voltage of the battery is sensed by azener diode and the output of the permanent magnet alternator iscontrolled thereby to maintain the battery voltage at a predeterminedlevel.

In some systems, batteries are not utilized and consequently, a readilyutilizable voltage standard for regulating the alternator output is notavailable. Nonetheless, it may still be desirable to regulate the outputof the alternator. For example, consider a vehicle having a permanentmagnet alternator for providing electrical energy to the lighting lampsof the vehicle. It will be appreciated that it is desirable from asafety standpoint to limit the power to the lamp to prevent prematurelamp burn-out. It is also desirable, in addition to the above safetyconsideration, to regulate the generator output to control the intensityof the light emitted by the lamp.

The present invention provides a solid state circuit of relatively fewcomponents for regulating the power output of an electrical powergenerator such as a permanent magnet alternator. The regulating circuitpreferably includes a solid state switch such as an SCR which isconnected across the output windings of the permanent magnet alternatorin parallel with the load, and a control circuit connected to the gateof the SCR for varying the firing angle of the SCR so that the SCRrepresents a varying impedance in parallel with the load. The controlcircuit is connected to one terminal of the output windings of thepermanent magnet alternator through a diode so as to receive positivehalf cycles of the alternator output waveform. The positive half cyclesare delivered through a voltage-limiting resistor to a first capacitorwhich is connected to the other terminal of the generator output windingso as to integrate each positive half cycle, i.e., to provide anintermediate signal having a potential peak which lags the potentialpeak of the half cycle waveform at the cathode of the diode. Forexample, the circuit values may be selected so as to provide anintermediate signal at low alternator speeds having a potential peakwhich is shifted with respect to the potential peak of the half cyclewaveform from 90 to slightly more than 160 of the alternator outputcycle to provide a monotonic waveform for slightly more than 160 of thealtemator cycle during which the SCR may be fired. Consequently, gradualregulation can be accomplished since the regulating circuit is capableof controlling the out put power by shunting the output winding of thealternator for only a small portion of each alternator output cycle,i.e., for less than 20 thereof, rather than making large reductions onspaced cycles. Consequently, large power fluctuations which cause lampflicker are avoided.

Insofar as the SCR is fired upon the attainment of a particularamplitude at its gate, and the amplitude of 1 the gating signal is afunction of the amplitude of the output of the alternator, the firing ofthe SCR is advanced in accordance with increases in the amplitude of thealternator output waveform, regardless of changes in the speed of thealternator. In this regard, the efficiency of an alternator increaseswith decreasing alternator temperature such that the amplitude of thealternator output increases with decreasing temperature although nochange in alternator speed occurs.

The preferred regulating circuit also includes a parallel circuit of aresistor and a second capacitor which is connected between the firstcapacitor and the gate of the SCR. As the alternator output frequencyincreases, the rate of increase of the intermediate signal with respectto the a ternator cycle decreases, tending to delay the firing of theSCR while an advance in the firing of the SCR is called for since thealternator output power is increasing. The parallel circuit of thesecond capacitorand the resistor offsets this tendency by establishing acombined path to the gate for the intermediate signal which has adecreasing impedance as the frequency of the alternator outputincreases. This decreasing impedance with frequency increases theamplitude of the gating waveform so that the SCR is gated atincreasingly earlier times with increasing frequency.

Also, as the alternator speed increases, the interme' diate signal willexperience a boost in DC offset, determined in accordance with the RCtime constant of the circuit having the first capacitor, since the firstcapacitor will not have sufficient time to discharge. The latter effectis additive to the effect of the decrease in the impedance of the pathfrom the first capacitor to the gate of the SCR to advance the firing ofthe SCR with increasing frequency.

In view of the above, it will be appreciated that changes in alternatoroutput power, whether or not the result of changes in alternator speed,are accommodated. The regulator of the present invention responds tosuch changes so as to limit the variations in power delivered by thealternator to a load.

It can be seen from the above that a circuit of relatively fewcomponents'is provided by this invention which effectively accomplishespower regulation of a permanent magnet alternator. It will beappreciated that the circuit is manufacturable at low cost using solidstate components to provide a durable and reliable regulating circuitwhich is especially suitable for use in the harsh environment of arecreational vehicle.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a circuit diagram of anexemplary regulating circuit according to the present invention;

FIG. 2 is a graph illustrating a typical output waveform of a permanentmagnet alternator;

FIG. 3 is a graph illustrating the change in the resistance of atungsten filament lamp as a function of excitation;

FIG. 4 is a graph illustrating the power dissipated in a permanentmagnet alternator as a function of alternator speed;

FIG. 5 is a graph illustrating the power dissipated in a resistive loadas a function of alternator speed;

FIG. 6 is a graph illustrating alternator efficiency as a function ofalternator speed;

FIG. 7 is a graph illustrating a generalized control signal incomparison with a generalized alternator output signal for a firstalternator speed.

FIG. 8 is a graph illustrating a generalized control signal incomparison with a generalized alternator output signal for a secondhigher alternator speed; and

FIG. 9 is a graph illustrating the equivalent impedance of anintermittently shunting SCR as a function of the angle of conduction ofthe SCR- with respect to the alternator output cycle.

FIGS. 10 and 11 are illustrations of additional embodiments of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1, a regulatingcircuit 10 is illustrated which is connected across the windings 12 of apermanent magnet alternator at terminals 14 and 116. The alternator maybe along the lines of that disclosed in the aforementioned patent toCarmichael, et al. A load R, which may be the tungsten filament of anillumination lamp, is connected in parallel with the regulating circuit10 and the output windings 12. The regulating circuit 10 includes an SCR18 and a control circuit 20, each of which is connected directly betweenterminals 14 and 16. The SCR 18 provides a shunt path for the permanentmagnet generator windings 12 when the SCR 18 is conductive.

The control circuit 20 includes a diode 22 which is connected to oneterminal 14 to provide the positive half cycles of the alternator outputwaveform at its cathode which are received by a voltage divider networkcomprising resistors RI and R2 so as to provide positive half cycles ofreduced potential at terminal 24. A first waveform modifying networkcomprising resistor R3 and Capacitor C 1 provides an intermediatewaveform at a terminal 26 having a configuration and purpose to bedescribed in detail hereinafter. A second waveform modifying networkcomprising a resistor R4 and capacitor C2 connects the terminal 26 tothe gate of the SCR 18 to provide a gating signal for the SCR 18 whichwill also be described in greater detail hereinafter. An adjustableresistor R5 establishes an appropriate control circuit output impedancewhich matches the'gate input impedance of the particular SCR used. Theresistor R5 is also used to fine tune the regulating circuit 10 afterassembly, as will also be more fully described hereinafter.

To aid in understanding of the operation of the regulating circuit 10 ofFIG. 1, the various alternator and load operating conditions, whichinfluence the operation of the regulating circuit, will be initially setforth.

In FIG. 2, a typical output waveform of a low cost permanent magnetalternator is illustrated. As can be seen in FIG. 2, the output waveformis distinctly nonsinusoidal and has significant energy in the oddharmonics. It can be seen that the initial positive monotonic portion ofthe curve occurs for less than the first 90 of the operating cycle ofthe alternator. In fact, the

output waveform of a typical permanent magnet alternator is even morecomplex thansuggested by the chart in FIG. 2 since the configuration ofthe waveform varies with the alternator speed, i.e., frequency. Also,the output waveform generally increases in amplitude as alternator speedincreases.

The operation of a regulating circuit for a permanent magnet alternatormay also be dependent upon changes in the load impedance. For example,as illustrated in FIG. 3, the tungsten filament lamp has a positivetemperature coefficient of resistance with excitation voltage so thatthe resistance of the lamp filament will increase as the voltage appliedto the lamp filament increases.

With reference now to FIG. 4, the next factor to consider is the powerdissipated in the alternator. Since permanent magnet alternators aresubject to frequency-dependent losses in the iron and magnet structure,the air gap, the windings, and are further subject to losses due tostray reactances, the output power of the alternator does not varylinearly with alternator speed. Typical variations in the power lossesof permanent magnet alternators as a function of speed are shown in FIG.4. As can be seen in the figure, the losses within the alternatorincrease relatively rapidly with alternator speed, especially for lowload impedances. Consequently, as seen in FIG. 5, the power provided tothe load decreases with alternator speed. Therefore, as seen in FIG. 6,the efficiency of the alternator, defined as the percent powerdissipated in the load with respect to the total power dissipated in theload and the alternator, decreases with increases in alternator speed.

In summary of the above, the configuration or shape of the alternatoroutput waveform, the amplitude of the alternator output waveform, theload impedance, and the internal alternator impedance, vary withalternator speed. Each of these variations affect the power delivered tothe load. Consequently, if power delivered to the load is to be closelyregulated, each of the above variations must be accommodated by thealternator regulating circuit.

The operation of the regulating circuit 10 of FIG. 1 will be consideredin the light of the graphs of FIGS. 7A and 7B which are illustrative ofgeneralized operational waveforms. It is cautioned that the waveforms ofFIGS. 7A and 7B are not fully representative of true waveforms, butrather, have been simplified to facilitate an understanding of thepresent invention. As one. example, it will be readily apparent that thesinusoidal waveform shown in each of the figures, incorporated torepresent the alternator output waveform, would more closely resemblethe waveform shown in FIG. 2.

As previously stated, the potential at the cathode of the diode 22represents the positive half cycles of the output waveform. Thispotential is reduced by the voltage divider network comprising resistorsRI and R2 to some value less than full value, for example, approximatelypercent of the full value. The first signal modifying circuit comprisingthe resistor R3 and the capacitor C1 integrates the reduced positivehalf cycle waves so that the peak of the intermediate signal at terminal26 lags the peak of the half cyclewaves at the cathode of the diode 22.The wave at terminal 26 is represented in FIG. 7A as the lower waveformwhich is monotonic and increasing for approximately 162 of thealternator cycle. Consequently, the initial positive monotonic portionof the intermediate signal at terminal 26 is extended substantially overthat of the signal at the cathode of the gate 22.

Considering for illustrative purposes that a network without reactiveimpedance connects the terminal 26 to the gate of the SCR 18 so that thelower signal of 5 FIG. 7A is provided to the gate of the SCR 18, it canbe seen that a monotonic signal, i.e., one which is suitable for gatingthe SCR 18, is available for a sufficient portion of the alternatoroutput cycle so that the output can be regulated by shunting the outputthrough the SCR 18 for as little as approximately 20 of the alternatoroutput cycle. If it were not for the lag in the occurrence of the peakof the intermediate signal at terminal 26, it would be necessary toshunt the alternator output for a minimum of 90 of the alternator cycleso that the minimum power regulation which could be effected would be ata reduction in the power output of the alternator consequent theshunting of at least 90 of the alternator cycle. Accordingly, a moregradual decrease in the power output of the alternator can beaccomplished with the circuit of the present invention.

Still considering the terminal 26 as being connected to the gate of theSCR 18 through a network without reactive impedance, it will beappreciated that as the amplitude of the output waveform of thealternator increases, the amplitude of the signal at terminal 26 willincrease so as to reach the gating level of the SCR at an earlier pointin time, and consequently, so as to advance the firing of the SCR tocorrespondingly reduce the power delivered to the load. Therefore, powerregulation is accomplished as a function of the amplitude of thealternator output. The response of the regulating circuit to theamplitude of the alternator output waveform can be conveniently adjustedby adjusting the values of the voltage divider resistors R1 and R2 toestablish the desired relationship between alternator output potentialand the gating potential of the SCR 18.

With increasing frequency, the lag of the peak of the signal at terminal26 with respect to the half cycles at the cathode of the diode 22increases somewhat. Also, the attenuation of the signal increases sincethe impedance of the signal path through the capacitor C1 decreases.However, although the attenuation of the signal is increased, the actualdiminution of the amplitude of the signal at the terminal 26 is offsetby the increasing amplitude of the alternator output waveform. Addi'tionally, the RC time constant of the circuit having the capacitor C]may be sufficiently long such that as the frequency increases, thecapacitor C1 will not fully discharge before the next charge cycle isinitiated. Consequently, a DC offset will occur which increases withincreasing frequency to actually increase the intermediate signal atterminal 26 with increasing frequency. However, the DC offset does notprovide an advance in the firing angle of the SCR 18 which is sufficientto offset the increasing power output of the alternator with alternatorspeed.

The second signal modifying circuit comprising the capacitor C2 andresistor R4 is used to advance the peak of the waveform at the gate ofthe SCR 18 with increasing frequency to fire the SCR 18 at increasinglyearlier times to accommodate increases in the power output of thealternator with alternator speed. More specifically, the parallelconnection of the capacitor C2 with the resistor R4 increasingly reducesthe impedance of the path from the terminal 26 to the gate of the SCR 18with increasing frequency whereby the signal level at the gate isincreased. As can be seen in FIG. 7B, the firing point is advanced toapproximately of the operating cycle of the alternator and will continueto advance with increasing alternator frequency to nearly 45 of thealternator output cycle.

When the gate fires at the peak shown in FIGS. 7A and 7B, the potentialsupplied to the regulating circuit is reduced by the shunting of thealternator output windings so that substantially no further increase ingate signal occurs. If it were not for the firing of the gate at thatpoint, a slight increase in signal may have occurred before the chargingof the capacitor C l ceases, i.e., when the potential supplied to thecapacitor Cl is no longer greater than the potential stored at thecapacitor C1.

When the SCR 18 fires, the output of the alternator is reducedsubstantially to zero so that the capcitor Cl begins to dischargethrough resistors R2 and R5. The discharge is at a rate established bythe values of the capacitor C1 and the resistors R2 through R5 so as toestablish the downward slope in the gate signal curve of FIGS. 7A and7B. The capacitor will continue to discharge until it again is suppliedwith a potential from the alternator 12 which is greater than itsinstantaneous charge.

As will be apparent from the previous discussion, the values ofcapacitor C1 and the resistor R3 are selected in combination with theother circuit components to provide a time constant which, at the loweroperating frequencies of the alternator cause the peak of theintermediate signal at the terminal 26 to occur at nearly of thealternator operating cycle, for example, at approximately 162 of thealternator cycle. The values of the capacitor C2 and the resistor R4 areselected to provide an advance in the firing of the SCR 18 withincreasing frequency in accordance with the operating parameters of theparticular alternator and the characteristics of the load so that thepower delivered to the load remains relatively constant. The resistorR5, as previously stated, is generally selected to provide anappropriate control circuit impedance at the gate of the SCR 18.Additionally, the resistor R5 is adjustable so as to finely tune theregulating circuit after assembly so that a high degree of accuracy inregulation is obtained. Since the gate of the SCR 18 has a relativelylow impedance, preferably, the resistors R1 through R5 have relativelylow values of resistance.

As will be appreciated in view of the above description, the regulatingcircuit 20 varies the angle at which the SCR 18 fires with respect tothe alternator cycle. This variation in conduction angle appears to thealternator like a varying load which is in parallel with the normalload. More specifically, as the generator output increases, the varyingload increases, i.e., its impedance decreases, thus holding the poweravailable to the normal load relatively constant. As can be best seen inFIG. 8, the SCR l8 equivalent impedance falls ofi rapidly as theconduction angle at firing increases to approximately 90 and falls offless rapidly thereafter. Referring now to FIG. 5, it can be seen thatthe power dissipated in the load when the alternator is unregulatedrises rapidly initially and less rapidly as alternator speed increases.Consequently, it can be seen how the control circuit 20 can be adjustedsuch that the SCR equivalent impedance decreases rapidly initially inaccordance with the rapid initial power increase at the alternator,

and less rapidly with the less rapid power increase at the alternator asthe alternator speed increases so as to be matched to the alternatorpower characteristics so that the load receives substantially constantpower.

In an exemplary operating embodiment of the present invention, thefollowing circuit values and components were used:

In the above exemplary embodiment, the resistors R3, R4 and R5 wereprovided by depositing a resistive, thick film ink on a ceramicsubstrate. The resistive film of the resistors R4 and R5 have selectedtemperature coefficients of resistance so as to compensate forvariations in the firing sensitivity of the SCR 18 with temperature sothat the SCR 18 will fire at a given potential at terminal 26substantially regardless of variations in the operational conditions ofthe SCR 18 which affect its temperature. In this regard, the resistivefilm of the resistor R5 has a negative temperature coefficient ofresistance while the resistive film of the resistor R4 has a positivetemperature coefficient of resistance. Since the resistor R4 isessentially in series with the gate of the SCR 18 and the resistor R5 isessentially in shunt with the gate of the resistor of the SCR 18, theeffects of the temperature coefficients of resistance of the resistorsand additive, i.e. effect of each on the firing sen sitivity of the SCR18 is in the same sense. If the temperature sensitivity of the SCr 18 issufficiently small, either the resistor R4 or the resistor R5 may have azero temperature coefficient of resistance.

In the calibration of the regulator 10, the resistor R5 is first trimmedso as to provide a predetermined firing sensitivity of the SCR 18 involts and milliamperes at the junction of the resistors R4 and R5.Thereafter, the resistor R4 is trimmed so as to provide a predeterminedfiring sensitivity of the SCR 18 at the terminal 26.

In FIG. 9, a full wave regulator is illustrated in combination with aresistive load R which may be a lighting lamp and a battery 32 which isconnected to the output winding 12 of the alternator by a full waverectifying bridge consisting of diodes 30-36. The full wave regulatoressentially comprises a pair of half wave regulators l0 and which areconnected in parallel and in opposite polarity relationship. Each of theregulators 10 and 10 are essentially as described with respect to theregulator 10 of FIG. 1 except that the values of the components areadjusted so that the shunting of each half cycle occurs at a time laterthan the time of shunting of a half wave regulator in accordance withthe increased regulating effect provided by full wave regulation. As canbe seen in the figure, the regulator 10 is connected to the winding 12to shunt on one half cycle of the alternator output while the regulator10' is connected to the winding 12 to' shunt on the other half cycle ofthe alternator output.

In FIG. 10, a voltage regulator 40 according to this invention isillustrated in combination with a battery 42, a rectifying diode 44, andlighting or lamp load R The regulator 40 is like the regulator 10 ofFIG. 1 except that it additionally includes a Zener diode Z1 to providehigh voltage transient protection. For example, high voltage transientsmay occur upon opening of a starter motor switch or other load switch.As can be seen in the figure, the Zener diode Zil is connected betweenthe cathode of the diode D1 and the gate of the SCR 18 so that a voltageexceeding the Zener diode voltage, for example, 200 volts, at thecathode of the diode D1 will cause substantially instantaneous firing ofthe SCR 18 so as to absorb the transient in the SCR l8. A Zener diode isselected which has a breakdown voltage which is lower than the peakvoltage rating of all other devices subject to excess transient voltagedamage. Consequently, solid state devices or other devices connected tootherwise receive the voltage transient are protected. It will beappreciated that a pair of the voltage regulators 40 having the highvoltage transient protecting diode Z may be used in a full waveregulating circuit as shown in FIG. 9 so that both positive and negativehigh voltage transients are accommodated.

Although the regulating circuit of the present invention has beendescribed in combination with a permanent magnet alternator, thoseskilled in the art will appreciate that the teachings herein may beapplied to other types of electrical power generators, and especiallythose providing an output waveform having a cyclically variableamplitude. For example, the regulator of this system may be used toregulate the fluctuating DC from a rectifying circuit which is connectedto the output windings of a permanent magnet alternator. By way ofillustration, the regulating circuit 10 may be connected to the outputof a full wave bridge rectifying circuit which is connected to oppositeends of an alternator output winding, or may be connected to thecathodes of a pair of diodes connected to the opposite ends of theoutput winding of a permanent magnet alternator having a grounded centertap.

Considering the complexity of the parameters influencing the powerdelivered to the load which change with alternator speed, andconsidering the changes in alternator output which occur even withoutchanges in alternator speed, it will be well appreciated that the abovecircuit uses unexpectedly few components. Moreover, it can be seen thatthe control circuit is fully solid state, and consequently, can be builtfor the rugged environment of snowmobiles and other recreationalvehicles simply by encapsulating the components. It will also beappreciated that due to the wide range .of regulation provided by theregulating circuit 10' of this invention, large power fluctuations areavoided such that power ripple, as would cause lighting flicker, areminimized.

It will be appreciated by those skilled in the art that the preferredembodiment of the invention disclosed herein is susceptible tomodification, variation and change without departing from the properscope or fair meaning of the subjoined claims.

I claim:

1. A method for calibrating a regulating circuit for a permanent magnetalternator utilizing an SCR having a gate electrode comprising the stepsof:

depositing a resistive film which connects with said gate electrodehaving a temperature coefficient of resistance which is selected inaccordance with the firing sensitivity of said SCR; and

adjusting the value of said resistor generally at a predeterminedtemperature of said SCR by removal of a portion of said resistive filmso as to increase the resistance of said resistive film so that said SCRfires substantially at a predetermined gate signal level at saidpredetermined temperature.

2. A method for calibrating a regulating circuit for a permanent magnetalternator utilizing an SCR having a gate electrode comprising the stepsof:

depositing first and second resistive films which connect with said gateelectrode with each of said resistive films having a temperaturecoefiicient of resistance which is selected in accordance with thefiring sensitivity of said SCR; and

adjusting the value of said resistive films generally at a predeterminedtemperature of said SCR by removal of a portion of said resistive filmsso as to increase the resistance of said resistive films so that saidSCR fires substantially at a predetermined gate signal level at saidpredetermined temperature.

3. A method for calibrating a regulating circuit for a permanent magnetalternator utilizing an SCR having a gate electrode comprising the stepsof:

depositing a first resistive film in series with said gate electrode ofsaid SCR and a second resistive film in parallel with said gateelectrode of said SCR. each of said resistive films having a temperaturecoefficient of resistance which is selected in accordance with thefiring sensitivity of said SCR; and

adjusting the value of resistive films generally at a predeterminedtemperature of said SCR by removal of a portion of said resistive filmsso as to increase the resistance of said resistive films so that saidSCR fires substantially at a predetermined gate signal level at saidpredetermined temperature.

4. The method according to claim 3 wherein said SCR has a cathode andwherein said step of depositing said second resistive film includes thestep of depositing said second resistive film so as to connect said gateand said cathode.

UNITED STATES PATEN'l OFFICE CERTIFICATE OF CORRECTION Patent DatedNovember 12', 1974 Inventor(s) rge E. Gynn It is certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:

Line 10 of the Abstract, after "signal" insert a first capacitor forintegrating the half wave signal--. Column 2, line 25, "a tenator"should be --alternat0r--. Column 7, line 39, and" should be --are--;

line 41, "SCr" should be -'-SCR--.

Signed and seale d this 4th day of February 1975.

(-SEAL) Attest:

MCCOY M. GIBSON JR. c. MARSHALL DANN Attesting Officer Commissioner ofPatents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No,177 D d November 12, 1974 Inventor(s) rge E. Gynn It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Lirie 10 of the Abstract, after "signal" insert a first capacitor forintegrating the half wave signa1-. Column 2, line 25, "a tenator" shouldbe --a1ternator--. Column 7, line 39, "and' should be --are--; line 41,"SCr" should be --SCR-.

Signed and sealed this 4th day of February 1975.

(SEAL) Attest:

McCOY M. mason JR. c. MARSHALL DANN V Attesting Officer Commissioner ofPatents

1. A method for calibrating a regulating circuit for a permanent magnetalternator utilizing an SCR having a gate electrode comprising the stepsof: depositing a resistive film which connects with said gate electrodehaving a temperature coefficient of resistance which is selected inaccordance with the firing sensitivity of said SCR; and adjusting thevalue of said resistor generally at a predetermined temperature of saidSCR by removal of a portion of said resistive film so as to increase theresistance of said resistive film so that said SCR fires substantiallyat a predetermined gate signal level at said predetermined temperature.2. A method for calibrating a regulating circuit for a permanent magnetalternator utilizing an SCR having a gate electrode comprising the stepsof: depositing first and second resistive films which connect with saidgate electrode with each of said resistive films having a temperaturecoefficient of resistance which is selected in accordance with thefiring sensitivity of said SCR; and adjusting the value of saidresistive films generally at a predetermined temperature of said SCR byremoval of a portion of said resistive films so as to increase theresistance of said resistive films so that said SCR fires substantiallyat a predetermined gate signal level at said predetermined temperature.3. A method for calibrating a regulating circuit for a permanent magnetalternator utilizing an SCR having a gate electrode comprising the stepsof: depositing a first resistive film in series with said gate electrodeof said SCR and a second resistive film in parallel with said gateelectrode of said SCR, each of said resistive films having a temperaturecoefficient of resistance which is selected in accordance with thefiring sensitivity of said SCR; and adjusting the value of resistivefilms generally at a predetermined temperature of said SCR by removal ofa portion of said resistive films so as to increase the resistance ofsaid resistive films so that said SCR fires substantially at apredetermined gate signal level at said predetermined temperature. 4.The method according to claim 3 wherein said SCR has a cathode andwherein said step of depositing said second resistive film includes thestep of depositing said second resistive film so as to connect said gateand said cathode.